1. Field of the Invention
The present invention relates to heterogeneous catalysts on an Al.sub.2 O.sub.3 --SiO.sub.2 substrate for the metathesis of olefins and functionalized olefins.
2. Description of the Background
The metathesis of olefinic hydrocarbons is employed in the manufacture of specific olefins, dienes and polyenes and unsaturated polymers. Even olefins with functional groups are subject to the metathesis reaction, provided suitable catalysts are used. Of special importance is the metathesis of unsaturated fatty acid methyl esters, which are produced on large scale by transesterifying native fats and oils with methanol and are, thus, commercially available as parent compounds. The metathesis of these esters opens new simple access to intermediate products that are important from a chemical engineering point of view for the industrial production of surfactants, plastics, plasticizers, lubricants and a whole range of fine chemicals.
According to Bosma et al., Journal of Organometallic Chemistry, vol. 255 (1983), pp. 159-171, the metathesis of unsaturated esters can be performed on a Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 catalyst, which is activated with an organo-tin compound of the general formula SnR.sub.4. To manufacture the catalyst, .gamma.-Al.sub.2 O.sub.3 is impregnated with ammonium perrhenate.
Warwel, Erdol-Erdgas-Kohle, Petroleum, Natural Gas, Coal, vol. 103 (1987), pp. 238-45, describes industrial metathesis procedures, wherein predominantly Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 --, CoO-MoO.sub.3 /Al.sub.2 O.sub.3 and WO.sub.3 /SiO.sub.2 catalysts are used. Accordingly, only the Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 catalyst is already active at room temperature.
According to FR 2 521 872, the metathesis of functionalized olefins can be performed on Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 --SiO.sub.2 catalysts. The substrate contains preferably only 10 to 30% SiO.sub.2. According to this process, organic lead compounds of the formula PbR.sub.4 are used as activators.
In NL-A-84 03 051 the metathesis is preferably performed on SiO.sub.2 -rich supported catalysts. The Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 --SiO.sub.2 catalysts contain in the substrate preferably 65 to 90% SiO.sub.2. The activators used are preferably tin tetraethyl and tin tetrabutyl.
Unfortunately, in order to use catalysts effectively in metathesis reactions, it is, at present, necessary to use high concentrations or large amounts of catalysts. This is particularly true in the metathesis of unsaturated esters. In fact, there are no catalysts which are, at present, commercially feasible in the metathesis of unsaturated fatty acid esters.